AU2009266109B2

AU2009266109B2 - Process for operating a plant for producing calcined clay

Info

Publication number: AU2009266109B2
Application number: AU2009266109A
Authority: AU
Inventors: Nikola Anastasijevic; Edgar Gasafi; Frank Siewert; Dietrich Werner
Original assignee: Metso Metals Oy
Current assignee: Metso Metals Oy
Priority date: 2008-07-03
Filing date: 2009-06-13
Publication date: 2014-07-10
Anticipated expiration: 2029-06-13
Also published as: UA106588C2; EA018769B1; EA201100137A1; DE102008031165B4; AU2009266109A1; BRPI0913910B1; DE102008031165A1; BRPI0913910B8; BRPI0913910A2; WO2010000383A1

Abstract

The production of calcined clay is effected by using a plant known per se for producing cement by the dry or semiwet process, with a precalciner (1), for instance comprising at least one preheating line of series-connected preheating stages (2), such as cyclone preheaters or grate preheaters, and a rotary kiln or roaster (3). In accordance with the invention, the rotary kiln or roaster (3) for generating heating gas is utilized as combustion chamber (31), replaced by a combustion chamber (3') and/or completed by an additional combustion chamber.

Description

WO 2010/000383 PCT/EP2009/004271 Process for Operating a Plant for Producing Calcined Clay 5 This invention relates to a process for operating a plant for producing calcined clay. At present, cement primarily is made of ground cement clinker, which is, however, very energy-intensive and leads to high CO 2 emissions. Beside the CO 2 emission from the combustion for achieving the clinker temperature as high as about 1450*C, CO 2 is 10 separated and emitted from limestone - the main raw material of clinker production. One possibility for reducing CO 2 emissions is the admixture of cement substitutes, such as calcined clay. Conventional plants for cement production by the dry or semidry process consist of a 15 precalciner (for instance series-connected cyclone preheaters) and a succeeding rotary kiln, alternatively a grate preheater (Lepol process) in the semiwet process. Calcining fine-grained mineral solids, such as clay, conventionally is effected in rotary kilns or multiple-hearth furnaces. This ensures the maintenance of a low temperature 20 with a retention time necessary for treatment in this process. U.S. patent 4,948,362 for instance describes a process for calcining clay, in which kaolin clay is treated in a multiple-hearth furnace by means of a hot calcining gas to increase gloss and minimize abrasiveness. In an electrostatic precipitator, the calcined clay powder is separated from the waste gas of the calcining furnace and processed to obtain the desired prod 25 uct. Due to the described demand of calcined clay for cement production, an inexpensive production process herefor is of particular interest. It is the object of the present inven tion to satisfy this demand close to the place of cement production. 30 This object in particular is solved with the invention in that for manufacturing calcined clay, the plant for producing cement by the dry or semiwet process is used itself, with a precalciner, for instance comprising at least one line of series-connected preheating - 2 stages, such as cyclone preheaters or grate preheaters, and a rotary kiln or roaster, wherein in accordance with the invention the rotary kiln or roaster for producing heating gas is utilized as combustion chamber, replaced by a combustion chamber and/or completed by an additional combustion chamber. The heating gases are 5 used for calcining clay and are guided through the preheating stages in counterflow to the solids. In accordance with the invention, an existing cement plant thus can be converted to operation for calcining clay at low cost by using the existing precalcining stages. 10 In an embodiment of the invention, there is provided a process for producing calcined clay in a plant for producing cement by the dry or semi-wet process, said plant including (i) a precalciner comprising at least two preheating lines of series connected preheating stages, wherein the one preheating line serves for preheating 15 the clay and the other one serves for heating clinker raw material, and (ii) a rotary kiln or roaster, wherein the rotary kiln or roaster for producing heating gas is utilized as combustion chamber, replaced by a combustion chamber and/or completed by an additional combustion chamber, 20 wherein the clay to be calcined is guided through the precalciner in counterflow to the heating gases of the combustion chamber and is heated by the heating gases to a temperature of up to 900 0 C, wherein the clinker raw material is heated by the heating gases of the combustion chamber, and 25 wherein the combustion residues obtained in the combustion chamber(s) are added to the calcined clay. The clay preferably is heated by the respective combustion chamber heating waste gases to a temperature between 650 and 850OC; with a corresponding retention 30 time, these temperatures are sufficient to completely calcine the clay. In accordance with the invention, it may be advantageous when preheating is effected in at least two preheating lines, wherein the one preheating line serves for preheating the clay and the other one for heating clinker raw material. 5177519_1 (GHMatters) P85767.AU - 3 A particularly flexible operation is possible when beside the rotary kiln or roaster for cement production an additional combustion chamber is operated, to which a separate heating line for the clay possibly is associated. 5 In a further aspect of the invention, a fuel/air mixture can be supplied to the heating gas stream of the respective combustion chamber before entry into the preheating line, so that enough heat is available in the possibly two or more preheating lines. For the purpose of a flexible and economic utilization of the process of the invention, 10 the fuel and/or air supply for the respective combustion chamber can be controllable. In the rotary kiln or roaster, relatively poor fuels, such as coal, carbonaceous minerals with sufficiently positive calorific value, biomass, sewage sludge and/or wastes can be used, which further increases the economy of the process. 15 Further objectives, features, advantages and possible applications of the invention can be taken from the following description of embodiments and the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, also independent of their inclusion in individual claims or their 20 back-reference. The only Figure illustrates an example for performing the process of the invention. The illustration in the only Figure represents the fundamental principle of the 25 operation of a plant for producing cement. The same includes a precalciner 1 with a plurality of preheating stages 2, which for instance can be formed as cyclone preheaters. Furthermore, it includes a rotary kiln 3, which in accordance with the invention can, however, (also) be operated as combustion chamber 3' by supplying fuel and air. To the heating gas obtained in the combustion chamber 3', a fuel/air 30 mixture can be supplied before entry into the precalciner 1. As a result, heating of the clay to be calcined, which is added as solid in counterflow to the heating gases, can be effected up to 900'C, preferably to 650 to 850C. Variants of the process shown in the drawing in particular consist in that either to the 35 one rotary kiln 3 with one preheating line a combustion chamber 3' additionally is 5177519_1 (GHMatters) P85767.AU - 3a associated or that to the one rotary kiln 3 operated as combustion chamber 3' at least two preheating lines from preheating stages 2 are associated, wherein for instance in the one preheating line clinker raw materials are preheated and in the other preheating line the clay to be calcined is preheated. To make this process 5 more flexible, combinations of these variants can also be used. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 10 In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not 15 to preclude the presence or addition of further features in various embodiments of the invention. 5177519_1 (GHMatters) P85767.AU WO 2010/000383 PCT/EP2009/004271 -4 List of Reference Numerals 1 precalciner 2 preheating stages 5 3 rotary kiln or roaster 3' combustion chamber

Claims

1. Process for producing calcined clay in a plant for producing cement by the dry or semi-wet process, said plant including 5 (i) a precalciner comprising at least two preheating lines of series connected preheating stages, wherein the one preheating line serves for preheating the clay and the other one serves for heating clinker raw material, and (ii) a rotary kiln or roaster, wherein the rotary kiln or roaster for producing heating gas is utilized as combustion 10 chamber, replaced by a combustion chamber and/or completed by an additional combustion chamber, wherein the clay to be calcined is guided through the precalciner in counterflow to the heating gases of the combustion chamber and is heated by the heating gases to a temperature of up to 900 0 C, 15 wherein the clinker raw material is heated by the heating gases of the combustion chamber, and wherein the combustion residues obtained in the combustion chamber(s) are added to the calcined clay. 20

2. The process according to claim 1, characterized in that the clay to be calcined is heated by the heating gases to a temperature between 650 and 850C.

3. The process according to any one of the preceding claims, characterized in that beside the rotary kiln or roaster for cement production an additional combustion 25 chamber is operated, to which possibly a separate preheating line for the clay is associated.

4. The process according to any one of the preceding claims, characterized in that a fuel/air mixture is supplied to the heating gas stream of the respective 30 combustion chamber before entry into the respective preheating line.

5. The process according to any one of the preceding claims, characterized in that the fuel and/or air supply for the respective combustion chamber is controllable. 5177519_1 (GHMatters) P85767.AU - 6

6. The process according to any one of the preceding claims, characterized in that in the respective combustion chamber coal, carbonaceous minerals with sufficiently positive calorific value, biomass, sewage sludge and/or wastes are burnt. 5

7. A plant for performing a process according to any one of the preceding claims, comprising a precalciner with at least two preheating lines and a rotary kiln and/or roaster operable as combustion chamber and/or a combustion chamber for generating heating gas wherein the one preheating line serves for preheating the clay and the other one serves for heating clinker raw material. 10

8. A process for operating a plant for producing calcined clay substantially as herein described with reference to the accompanying figure. 5177519_1 (GHMatters) P85767.AU